1. Field of the Invention
This invention relates to a fiber optical measuring device and has particular utility in the measuring of electrical and magnetic quantities such as voltage or magnetic field. The measuring device comprises a measuring electronic unit, a transducer having a sensor element, and at least one optical fiber means connecting the transducer to the measuring electronic unit. The measuring electronic unit includes at least two light source means having separate emission spectra for excitation of photoluminescence in the sensor element and at least one photo-detector means for detecting photo-luminescence emanating from the sensor element.
Throughout this specification the term "light" is used to denote electromagnetic radiation in the vicinity of the visible spectrum, but it should be understood that the term includes electromagnetic radiation in the infrared and ultraviolet regions.
2. Description of Prior Art
In a power system there is a great need to measure electrical currents and voltages by means of optical fibers in a simple, inexpensive and reliable manner. Systems for measuring such quantities are already known and tested--see, for example, U.S. Pat. No. 4,290,146 and U.S. patent application Ser. No. 83,273, filed Oct. 10, 1979 (now abandoned). However, with today's technology such known systems have been found to have electronic or mechanical sensing systems which, to be reliable, are complex and thus expensive. It is desirable in this connection to be able to provide a simple and reliable sensor which, when placed at the end of an optical fiber, is able to sense an electric voltage, an electric current or a magnetic field and which, with great accuracy and speed, is able to convert these quantities into an optical signal.
One possibility for a system to achieve this aim is to measure a current by means of a light-emitting diode (LED), whereby the temperature-dependence of the LED can be compensated for by a simultaneous measurement of the spectral distribution of the emission spectrum--see U.S. Pat. No. 4,378,496. However, with such a known measuring system, the aging phenomena in the LED must be controlled which, at the present time, is difficult to combine with the requirement to provide an inexpensive measuring system. The main problems as regards the aging of LEDs are to be found in the crystal faults, caused by the injection current, in the light-emitted region and in an increasing number of non-radiant recombinations at the PN junction by the diffusion therein of deep recombination centers, as, for example, Cu.sup.+.